In hospital and laboratory settings, there are three primary methods of sterilization currently used. These are steam sterilization, ethylene oxide gas sterilization, and dry heat sterilization. It is well known to apply sterilant-sensitive inks to the package or article to be sterilized so that the end user can readily determine whether or not the package has been exposed to the sterilization process. Some inks indicate exposure only, while others are capable of indicating the degree of sterilization, i.e. whether or not the package has been sufficiently exposed.
For the steam sterilization process a typical ink monitor formulation comprises sulfur (or a sulfur-containing compound), a metal salt and a solvent into which the first two components are suspended. While this type of formulation is suitable for steam processes which may be carried out from between about 250.degree. F. and 270.degree. F., it is not sensitive to the ethylene oxide gas sterilization process.
U.S. Pat. No. 3,627,469 discloses ink formulations comprising selected substituted pyridenes, quinolines and isoquinolines useful as exposure and sterilization monitors. These compounds are typically dissolved or suspended in organic solvents and have been found to be sensitive to ethylene oxide gas and dry heat sterilization processes as both exposure and sterilization monitors. These formulations are not, however, sensitive to steam sterilization processes.
An ink formulation suitable as a sterilization monitor for steam, ethylene oxide and dry heat sterilization methods would be a useful addition to the art.